The CV5808 (E55L) all glass special quality pentode from Mullard was designed as a high gain low impedance video/wide-band output valve and found use in top quality oscilloscopes.
The Mullard description of this valve is 'Special quality high slope output pentode intended for general industrial applications where stability of characteristics and long life are required.
The data sheets give absolute maximum ratings and these appear in the second table. Additionally for operation with a shorter life the maximum cathode current can be extended to 100 mA. The bulb maximum temperature can also be increased from 180 °C to 220 °C under reduced life conditions.
The gm has a very high value, which both makes the wide-band capabilities possible and makes testing of used valves difficult.
Visual inspection shows that within the anode cavity are beam plates even though the device is quoted as a pentode. The screen grid is formed from a parallel series of very fine wires. The control grid is too close to the cathode to be seen. As is typical of special quality valves the base pins are gold plated to give low contact resistance and resist corrosion.
Looking along the grid axis. The bright beam plates are seen end-on. The fine wires of the screen grid are clear.
The Mullard logo, commercial Type designation and Made in Great Britain.
A closer view.
The wide glass tube envelope is 29 mm in diameter and, excluding the B9D base pins, is 57 mm tall.
Reference: Data-sheet & 3002. Type CV5808 was first introduced in 1960. See also1960 adverts.